"""Tenant ID resolution — TURNSTONE_TENANT_ID env var, hostname fallback."""
from __future__ import annotations

import os
import socket
from functools import lru_cache


@lru_cache(maxsize=1)
def resolve_tenant_id() -> str:
    """Return this node's tenant ID. Result is cached after first call."""
    return os.environ.get("TURNSTONE_TENANT_ID") or socket.gethostname()